In the field of surveying and distance measuring equipment, there is a need to determine the position of objects (markers, etc. ) relative to fixed points. There are several methods for doing this. In general, two approaches are used. One method involves the measurement of linear distances; another, the measurement of angles and distances. Usually a construction site is surveyed and the topography is plotted before work begins. Fixed flags tell the equipment operators to either cut or fill a particular location. An iterative process of survey and grade is used to work the site into the final topography prior to actual construction. This iterative process is slow and laborious and therefore expensive. Since there is a great deal of human work involved, it is also error prone.
The prior art describes many efforts to use modem electromagnetic technology to control the movement and action of earth moving devices. The most pertinent of these efforts known to the inventor is described in U.S. Pat. No. 5,076,690, to deVos et al., that discloses a sophisticated and ingenious system for locating an earthworking machine or handheld survey device and defining the direction of movement thereof. Triangulation between three bar-coded reflective plates positioned at known coordinates relative to each other around the periphery of a two-dimensional coordinate frame is accomplished by rotating a calibrated laser source to impinge upon and be reflected by the reflectors. A computer solves simultaneous equations based upon angular measurements to triangulate the position of the machine and, using a series of such triangulations, to define the direction of travel. While the deVos, et al., system appears to be quite suitable for working a small to moderate tract of relatively flat land, it has certain important limitations that are overcome by the present invention. First, the deVos, et al, system works in only one plane. Secondly, being reflective and requiting accurate readings of reflected bar codes, the system is limited to use on small tracts, i.e. , where the maximum distance from the machine or survey device to any reflector is not more than about 100 meters. There remains a serious need for systems that are suitable for use on hilly or uneven terrain and upon much larger tracts, such as are commonly worked in certain parts of the country and in large housing projects. It is to these needs that the present invention is primarily directed, though it may be used on tracts of any size or terrain.
Other prior art efforts are described in the following patents and publications.
U.S. Pat. No. 4,700,301, to Dyke, on Oct. 13, 1987, discloses a method of automatically steering agricultural type vehicles on a preprogrammed course by continuously measuring angles between reference points and using a microprocessor to calculate vehicle position and direction of motion.
U.S. Pat. No. 4,677,555, to Goyet on Jun. 30, 1987, describes a method and equipment for automatic guidance of earthmoving machines and especially machines for laying drainage elements. The machine consists in preliminary recording, in digital form and on a moving magnetic recording medium, of all the planimetric and altimetric data relating to the operations to be performed with reference to datum points and to reference plane. There are then placed on the ground of the drainage site fixed beacons for marking the location of the selected datum points as well as a rotating laser beam emitter for defining the desired reference plane. The crawler machine to be guided is equipped with a microprocessor control-module for reading the indications recorded on the magnetic recording medium and controlling two guidance devices, one device being employed for planimetric guidance of the crawler machine and the other device being employed for altimetric guidance of the drain-laying or digging tool of the machine. These two control devices produce action respectively on the steering control of the machine and on the system for controlling the height-setting of the tool with reference to the fixed locating beacons and to the plane defined by the rotating laser beam.
U.S. Pat. No. 4,537,259, to Funabashi on Aug. 27, 1985, describes a blade control device that comprises a change-over switch for providing light receiving position deviation signal sent out from a light receiving device into a light receiving device control system as a command value, and a device for measuring the change in the height of the light receiving device, whereby a topographic survey is conducted based on the height change of the light receiving device.
U.S. Pat. No. 4,413,684, to Duncklee, on Nov. 11, 1983, discloses a laser-controlled ground leveling device with overfill sensor and wheel rise limiting device for detecting when the box blade is full and overflowing is imminent and sensing the level of the box blade relative to the ground. The improvement overrides the functions of the conventional laser beam controls.
U.S. Pat. No. 4,402,368, to Moberly on Sep. 6, 1983, discloses an earth scraper and ground support therefor capable of self adjustment in accordance with a preestablished signal such as a laser beam, capable of grading cross sloping surfaces, capable of minimizing blade deflection caused by carrier wheels hitting a flaw in grade, and adaptable for highway towing along a single lane of a highway.
U.S. Pat. No. 4,299,290, to Nunes, on Nov. 10, 1981, describes a grading machine and blade moving structure that includes a grading blade supported by caster wheels and a laser sensor or receiver is carried by the grading machine for raising and lowering the grading blade as the receiver falls and rises in traveling across a field.
U.S. Pat. No. 4,273,196, to Etsusaki, on Jun. 16, 1981, discloses a beam receiver secured to an upper portion of a blade of an earth working equipment can rotate in a horizontal plane and move in a vertical direction and, accordingly, can catch a laser beam from a beam projector regardless of a direction of the equipment. When the beam has been deviated out of the beam receiver, the direction of the deviation is detected so that the beam can be received by the beam receiver again. The height of the beam receiver relative to the blade can be adjusted and the level of the blade can thereby be controlled very accurately.
U.S. Pat. No. 4,173,258, to Boulais, et al., on Nov. 6, 1979, disclose a laser beam level control with automatic override function to temporarily block blade-down signals and raise the blade when lowering it or leaving it at its previous height would increase the force required to drive the machine across the ground above a preselected value which does not exceed the tractional force capability of the machine's drive wheels or exceed the machine's available horsepower.
U.S. Pat. No. 4,751,782, to Ammann, on Jun. 21. 1988, discloses a beam levelling instruments that has a pipe length which is vertically and centrally mounted in the cover of a casing. The ends of this pipe length are pivotable, so that it can always be held in the vertical position. For this purpose two spirit levels are arranged at right angles to one another on a plate fixed to the lower end of the pipe length. The fluid in these levels is electrically conducting and the levels have electric contact points for operating a respective electric motor. The electric motors are provided with eccentric shafts which come into contact with the circumferential surface of the pipe length. If the pipe length diverges from the vertical, then the current from batteries ensures that it is brought back into the vertical position by means of the eccentric shafts. A laser light source is located in the lower part of the pipe length and a further pipe length is inserted in the upper end of the pipe length and can be rotated by a third electric motor. The further pipe length carries a head with a window. The laser beam enters the head vertically, is diverted there into the horizontal and passes out of the window as a horizontal laser beam.
U.S. Pat. No. 4,244,123, to Gelesko, on Jan. 13, 1981, describes a guidance device for drain tile laying machine having an improved guidance device for use with an earthworking machine more especially a drain tile laying machine, comprising a earthworking element mounted about a pivot connection. This guidance device comprises a signal emitter and two signal receivers mounted on the earthworking element of the machine. The two signal receivers are mounted on the dement in a longitudinal spaced apart relation, so as to distinguish between a depth change or an attitude change in the element. The guidance device also comprises operating means including an electronic control circuit and an hydraulic operating circuit for adjusting the attitude or depth of the element depending on the indication given by the signal receivers.
U.S. Pat. No. 4,836,669, to Teach, on Jun. 6, 1989, discloses apparatus and method project light in two orthogonal planes to provide reference planes of light for use in laying out a construction site or the like. The apparatus comprises a laser light source for providing a source beam of light, and a light diverting arrangement. The light diverting arrangement diverts a first portion of the source beam of light to project a first thin reference fan beam of light substantially in a first reference plane, and diverts a second portion of the source beam of light to project a second thin reference fan beam of light substantially in a second reference plane. The second reference plane is substantially perpendicular to the first reference plane.
U.S. Pat. No. 4,807,131, to Clegg, on Feb. 21, 1989, describes a fully automated earthgrading machine and system such as an earth grading system for grading a tract of land using a power driven earth grading machine, a laser beam generator remote from the earth grading machine for projecting a laser beam in a predetermined pattern relative to the earth to be graded. A laser detector is carried on the grading machine for receiving the laser beam and a computer is provided for calculating distances and the actual location of the grading tool relative to the continuum computed by the reference data signal and controlling the grading in accordance with a predetermined computer program.
U.S. Pat. No. 4,774,403, to Arts, on Sep. 27, 1988, discloses a position measuring device using a triangulation scheme for position sensing. A laser diode projects a spot upon a target surface. The image of the spot is focused on a charge coupled device linear image sensor. The image of the sensor is indicative of the distance from the device to the target surface.
U.S. Pat. No. 5,032,023, to Schneiter, on Jul. 16, 1991, discloses an apparatus for a variable depth triangulation ranging system, the ranging system including means for emitting a fight beam, means for focusing an emitted light beam on an object, and lens means for imaging reflected light onto an input end of said apparatus. The apparatus includes an optical fiber bundle, the bundle including an input end and an output end, the bundle input end being disposed so as to intercept transmissions from said lens means, means for scanning, in a time-based manner, the bundle output end, the scanning means being configured to generate a time-based signal indicative of a light signals present at the bundle output end, and means for calculating system geometry and range from the time-based signal.
Tanabe, Toru, Experimental Validation of GPS-INS-STAR Hybrid Navigation System for Space Autonomy, International Astronautical Congress, 39th, Bangalore, India, Oct. 8-15, 1988. 12 p. (Abst.) describes the gps-ins-star hybrid navigation system concept combines these three sensors: a ins-star hybrid system, a gps-ins system, and a gps-ins-star system. It was concluded that a star field simulator had been developed to serve as a source of radiation for the astro star tracker. A minimum of three simulated guide stars with variable magnitudes were needed to fully test the star tracker performance under simulated mission conditions.
Ward, J. E., Jr., (masters thesis) Dec. 1984, 170P, Report no.: AD-A151827, (Abst) described an autonomous state determination system developed for an earth orbiting satellite using horizon sensors and star trackers. The horizon sensors detect the earth and establish the local vertical reference, while either one or two star trackers make angular sightings of known stars.
Duncan, R., Report no. Nasa-tin-82203, (Abst) catalogs the angular separation of all star combinations for 148 NAV STAR on the onboard software for space transportation system-3 flight and following missions is presented as well as the separation of each pair that satisfies the viewing constraints of using both star trackers simultaneously.
Corson, R., Report no.: Nasa-tin-79515 (Abst), describes a space shuttle inertial measurement unit alignment algorithm. Three crew displayed parameters were considered: (1) the results of the separation angle difference (sad) check for each starpair; (2) the separation angle of each starpair; and (3) the age of each star measurement.
Van der Grinten, H. F., Navigation, vol. 22, Summer 1975, p. 128-134, (Abst), cataloged forty-six celestial lines of position obtained aboard a ship at sea are compared with the position as interpolated between NAVSAT fixes. Least squares adjustment of the combined celestial lines of position yielded a fix with an essentially circular error ellipse. The directional distribution of stars was well balanced. The navsat positions and the combined celestial fix were found to be substantially in agreement. Using the NAVSAT positions as a reference the mean error of well balanced celestial fixes as derived from the data and the method of least squares can be expected to be less than 0.8 nm for a 3-star fix and 0.1 nm for a 46-star fix. These results permit the construction of probability contours around well balanced celestial fixes consisting of various numbers of observations.
Wertz, J. R., Spaceflight, 14; June 1972, p. 206-216, (Abst) asserted that the most essential requirement is an atlas of the three-dimensional positions of all of the stars in the region to be explored and any bright navigational stars that might lie outside this region. In addition to accurate stellar positions, data about the velocities of the listed stars are required together with some means of accurately identifying individual stars--specifically, their absolute magnitudes and detailed spectra. Given the interstellar navigation atlas, there are many ways for the navigator to determine his position and velocity. Effects of high speed motion are discussed, together with the possibility of visual disorientation due to a displacement of the star field caused by small shiets of location.
A method for determining the position of an object in a 3D space has been proposed. An M-array LED pattern is projected onto the object through a lens and the projected array is observed with a CCD camera. Each element of the M-array is time modulated with an M-sequence having different phase. The cross-correlation function between the observed signal and the reference gives information about the phase, and thus the point-to-point correspondence. Then simple mathematical relations are used to determine the exact 3D position of the object. The proposed method is robust to noise and highly efficient. (Measurement of 3-dimensional position by use of M-array projection, Jing-Min Sham Kashiwagi, H.; Sakata, M., dournak Transactions of the Society of Instrument and Control Engineers, vol.25, no.4 p.389-95, 1989).
The monitoring of the motion of an arbitrary mandibular point has been accomplished using a recording system that includes three cameras. Each camera contains a cylindrical lens and a linear optosensor (CCD). Two extra-oral lightweight target flames (2 g) containing each three light emitting diodes are fixed on the patient's teeth. The system fires each LED cyclically and computes their three-dimensional coordinates in a reconstruction unit. From these coordinates another processing unit computes the three-dimensional coordinates of an arbitrary jaw point in a head fixed coordinate system. The computed trajectories are drawn on-line with the help of dedicated 3D viewing hardware on a CRT where they can be directly rotated and zoomed to follow intricate motion details. (Real-time, noninvasive recording and three-dimensional display of the functional movements of an arbitrary mandible point, Mesqui, F.; Kaeser, F.; Fischer, P., Proceedings of the SPIE--The International Society for Optical Engineering vol.602 p.77-84, 1986).
An optical correlator uses a light emitting diode array, in which analog signals from two spaced sensors are correlated in order to locate and track a target. One signal is clipped and digitized and clocked through a shift register, and the other signal is delayed. The shift register is coupled to an LED array, element for element. Each shift register element modulates its corresponding LED element. The delayed signal is also connected at its output to the LED array via a transistor, and modulates each LED element. Therefore, the LED elements emit light in proportion to the product of the two signals. The emitted light is focused onto a CCD imaging array where it is integrated over a period of time before being sent to an integrator and output display device. The output is the correlation function versus the time delay between the two signals. Successive outputs display the movement of targets. Circuit design mitigates inherent errors within the system. (Acoustic Signal Optical Correlator Using a Light Emitting Diode Array, Fogarty, E. J. U.S. Pat. No. 4,805,158, Feb. 14, 1989).
Sze, S., PHYSICS OF SEMICONDUCTOR DEVICES (2nd edition), Wiley-Interscience,New York, N.Y., 1981 (Abstr.) presents a resume regarding the physics and properties of semiconductors including photonic devices such as the LED and semiconductor lasers, photodetectors, and solar cells.
A helmet mounted sight system using CCD technology is described which can be used outside the restricted viewing area of the head up display, but with reduced accuracy. It is noted that the system consists of two pans: the helmet mounted display and the helmet optical position sensor. It is reported that a limited amount of essential information (i.e. aiming reticule, weapon lock, etc.) can be displayed on the surface of the helmet mounted display, noting that the limit is set by the pilot's inability to assimilate further data. Attention is given to the helmet optical position sensor which consists of two triads of LED's mounted on the sides of the helmet and two CCD cameras mounted in the cockpit. Finally, it is concluded that using the CCD to its full capability enables a small compact system to be produced without the need for fast analog to digital converters and a large digital store. (A helmet-mounted sight using C.C.D. technology, STEPHENSON, M.D., Radio and Electronic Engineer, vol. 49, Oct. 1979, p. 511-513, 1979).
U.S. Pat. No. 4,441,783, to Houghton, et al. on Apr. 10, 1984, described improved and inexpensive means for achieving uniform, luminous intensity over a sharply bounded horizontal arc of visibility, and also for achieving a desired vertical arc of visibility, comprise means for projecting light from a diffuse source or an array or mosaic of point sources into a field the horizontal and vertical arcs of which can be precisely defined. The disclosure encompasses two geometric configurations for projecting light, symmetrical and asymmetrical, compound parabolic concentrators, each of which may be constructed as either a reflective cavity or a refractive dielectric, thereby to provide four basic designs for achieving uniform illumination over various horizontal arcs of visibility. In addition, the disclosure encompasses three modes of diffuse light projection to achieve uniform illumination over various vertical arcs of visibility.
U.S. Pat. No. 5,043,924, to Hofmann, on Aug. 27, 1991, describes Method and apparatus for scanning an object transversely to the flight direction or direction of motion of the scanner with a detector row arranged perpendicularly to the direction of scanning.
U.S. Pat. No. 4,994,907, to Allen, on Feb. 19, 1991, describes a color sensing CCD with staggered photosites, e.g., a line sensor with photosites accurately located for color scanning. The sensor includes a plurality of photosites arranged in a two-dimensional, staggered pattern which is repeated across the length of the sensor. Only one photosite is located for every direction perpendicular to the axis of the line image. Individual color filters extend over all the photosites located at the same perpendicular distance from the line image axis. In one embodiment, the filters are disposed on separate transparent members which are aligned and assembled over the photosites.
Mollow, P. A., et al, Journal: Proceedings of the SPIE--The International Society for Optical Engineering, Vol.1347 p. 123-30, 1990 (Abstr.) describes a system using one-dimensional optical devices to perform the desired two-dimensional correlation. The two-dimensional correlation is performed as a series of multichannel time-integrating correlations between each input image line and a reference template that is stored in an electronic memory. The rows of the reference template are introduced into the processor in parallel using a one-dimensional laser diode array. The correlation in the vertical direction is performed using a modified charge-coupled device operating in the shift-and-add mode. Key features of the system include the random access template memory, the custom laser diode array consisting of 64 individually addressed laser diodes.
The basic mathematical formulation of a general solution to the extraction of three-dimensional information from images and camera calibration has been described. Standard photogrammetric algorithms for the least squares estimation of relevant parameters are outlined together with terms and principal aspects of calibration and quality assessment. Three-dimensional testfields and independently determined reference coordinates were used for quality assessment using off the shelf equipment to an accuracy of 1/20/ sup th/and 1/50/ sup th/ of the pixel spacing in row and column direction respectively has been achieved. The system was used to calibrate the vision system of a ping-pong playing high-speed robot tracking table-tennis balls with a 50 Hz rate. Calibration of CCD-cameras for machine vision and robotics, Beyer, H. A., Journal: Proceedings of the SPIE--The International Society for Optical Engineering vol. 1197 p.88-98, 1990 (Abstr). Two sensors were used in a system for autonomous rendezvous and docking manoeuvres in space. The first is a proximity sensor, which is dedicated for distance and angle measurements. The sensor's equipment consists of three units: the position-sensitive detector, the illuminator and the common optics including a c.w. laser rangefinder. On the target side a corresponding reflector complements the necessary equipment to measure distance and angle deviation from boresight direction. The operation wavelengths are between 790 and 850 nm. The second is a high-resolution CCD-camera in combination with a dedicated S/W processor, which is used for distances between 2 m and 100 m. On the target side, a three-dimensional symmetric pyramid reflector configuration is used. The camera processor transforms the actually depicted reflector configuration differences to the expected reflector configuration for boresight position into distance and position information for six DOF. This method can achieve faster update repetition rates ( 10 Hz) than a common pattern recognition technique. The camera is equipped with a 880 nm wavelength LED illuminator. Optical sensors for position measurements, Schroer, G. et al, Sensors and Actuators vol. 17, no.3-4p.329-38, 1989 (Abstr).
Optical correlators have been used to investigate real time pattern recognition. 1-D devices have been used to perform the two dimensional correlation in real time by using an array of light emitting diodes (LED's) to input an electronically stored reference image into the processor in parallel. The input scene data is introduced into the processor one line at a time using an acousto-optic device (AOD). Multichannel time integrating correlations are performed in the row direction using the AOD and in the column direction using a charge coupled device (CCD) operating in the time delay and integrate mode. A processor that correlates a 64.times.44 pixel binary reference image with a 256.times.232 input scene at video rates was used. A second correlator is a space integrating Fourier transform based correlator. A magneto optic-device (MOD) is used at the Fourier transform plane to rapidly change filter functions. Stalker, K., et al, International Congress on Optical Science and Engineering, 24-28 Apr. 1989 (Abstr).
In another application, a new sensor that can measure the two-dimensional environment of a robot has been reported. This sensor consists of a laser diode and a charge coupled device (CCD) linear array sensor built in a simple optical imaging system with a rotating mirror. The measuring range of this sensor is 250 mm to 6000 mm, and the measuring time for one direction is 1 ms to 10 ms. It can measure distances more than 200 points to obstacles or walls around robot per second. The position of the walls is recognized from these measuring points using a microcomputer system. Development of environment sensor for vehicle robot, Takamasu, Kiyoshi, Journal of the Robotics Society of Japan, Volume: 5, Issue: 3, Pages: 199-202, June 1987 (Abstr).
U.S. Pat. No. 4,970,653, to Kenue, on Nov. 11, 1990, discloses an image processing method that operates on an image from a CCD camera viewing a roadway scene in front of a vehicle to detect lane markers and determine the relationship of the vehicle to the lane. Obstacles in the lane near the vehicle are detected and a warning is given to the driver. The method uses template matching techniques or a hough algorithm to detect the lane markers or road edges.
The components and instruments necessary to carry out the present invention are available commercially. (Components and peripherals, buyers guide, EDN VOL.: v33 n15 p253(27), Jul. 21, 1988, Lasers & Optronics, v7, n4, p76(3), April, 1988.) For example, Infrared Associates' infrared detectors and related accessories have applications in analytical instruments, medical thermography, thermal imagers, air-borne scanners, high-altitude balloon experiments, laser range finders and high-speed missiles. They come in single and multi-element arrays and can be packaged in a variety of metal or glass dewars, which can be cooled or uncooled. The matched preamplifier circuits can be provided in single or multi-channel configurations. Infrared Associates, Inc., 1000 Route 130, Cranbury, N.J. 08512. Automated Waveform Digitizers LeCroy Corp.'s line of high-performance automated single-channel, waveform digitizers provides high speed wave measurement and analysis instrumentation. Among the benefits the devices provide are higher accuracy measurements, extended memory-length waveform recording, pre-and post-trigger waveform recordings, high resolution transient capture, digital signal processing and analysis and total programmability. LeCroy Corp., 700 Chestnut Ridge Rd., Chestnut Ridge, N.Y. 10977-6499. A Red-emitting diode laser is available in the visible-wavelength range. NEC's Model NDL 3200, operates at room temperature and will run more than 3,000 hours without performance degradation. Fabricated in indium gallium arsenide phosphide, the device emits a minimum of 3 milliwatts at 680 nanometers. The diode has a back-facet monitor photo-diode and is offered in a three-pin, 9-millimeter TO can. This diode laser has rise and fall times of 400 nanoseconds. NEC Electronics, Inc., P.O. Box 7241, Mountain View, Calif. 94039. The 4000 series of lasers from Continental Laser Corp. feature a two-tube tandem design which virtually eliminates any down time, according to the manufacturer. Two large-diameter solid Invar rods provide a 50-inch resonator structure for stability. The systems are designed for OEM, industrial, medical, entertainment and scientific applications. Multi-line power specifications are 8 to 12 W for the argon models and 2.5 to 4 W for krypton. Light regulation, prism wavelength selector, remote-control module and etalon assembly options are available. Continental Laser Corp., 805 E. Middlefield Rd., Mountain View, Calif. 94043. XMR Inc.'s Model 5100 excimer laser is designed specifically for a long lifetime of industrial use. Capable of generating a continuous 150 watts of average power or 200 watts for shorter periods, the 5100 features a magnetically switched PFN and can be incorporated into custom laser-based systems. XMR, Inc., 5403 Betsy Ross Dr., Santa Clara, Calif. 95054. Air- and water-cooled argon and krypton lasers, American Laser Corp., range in output power from 1 to 8 watts, continuous wave, multi-time configuration. The units are available in argon, krypton and mixed gas and offer additional features such as single-line operation, TEM sub.00, extended-life tube, tunability, UV and service contracts. American Laser Corp., 1832 S. 3850, W., Salt Lake City, Utah 84104. A hard-sealed, integral-mirror, plane-polarized helium-cadmium laser, the Model 43001, exhibits a typical polarization ratio higher than 1000:1. Measuring 4.times.4.times.24 inches with a full Invar resonator, this laser offers high power stability ([plus-or-minus]) 1 percent over one hour), low noise ([is less than or =]) 1 percent rms) and an extended warranty period (4000 hours or one year to half power). The laser is also available with random polarization or with frit-sealed, fused-silica Brewster windows for those users switching between 325 and 442 nm operation. Liconix, 1390 Borregas Ave., Sunnyvale, Calif. 94089.
A digital video CCD Camera and scientific investigations is available. This camera features high-resolution, true random triggering, high-light gain with optional image intensifiers, digital and standard video outputs, digital frame store and on-board video monitor, digital delay and exposure-time controls, and sequence operation for stroboscopic photography. Applications include ballistics, detonics and other high-speed photography including laser and fusion research and spectroscopy. Marco Scientific, Inc., 1055 Synnyvale-Saratoga Rd., #8, Sunnyvale, Calif. 94087.
A tunable CO.sub.2, computer-tuned laser oscillator with center--and offset-frequency locking provided by a built-in Stark cell. The Strak cell and frequency stabilizer can be used in any kind of ranable CO.sub.2 laser. Ultra Lasertech, Inc., 6415 Viscount Rd., Mississauga, Ontario, Canada L4V 1K8. A flashlamp-pumped Alexandrite laser, a CO laser and low-light-level laser receivers at are available from Photon Interactions, 5645E General Washington Dr., Alexandria, Va. 22312.
A recent terbium gallium garnet that has a low thermal conductivity and low optical absorption rate, useful in Faraday rotators that run in high-average power applications. It has a wide range of transparency, from 500-1500 nm, and low optical absorption. Allied-Signal Inc., Sales Department, P.O. Box 410168, Charlotte, N.C. 28241-0168.
Herschelian-mounted remote sensing receivers and radio-metric systems are available from Lambda/Ten Optics. They have Herschelian-mounted Newtonian telescopes and collimators. These all-reflective instruments have no central obscuration and locate the focal plane to the side of the collimator/telescope. Used as a collimator, the Lambda/Ten "NC Series" projects a collimated beam from the light source to infinity. As a telescope the unit images light from a distance to the focal plane. The series is ruggedized in a heat-treated aluminum tube, fully self-supporting, and mountable in any orientation. Lambda/Ten Optics, 1 Lyberty Way, Westford, Mass. 01886.
The present invention solves the problems left unresolved by the prior art generally and by deVos et al., supra, specifically, namely the problems of locating a point on the surface of very large tracts of hilly or otherwise uneven land. A principal application of the invention will be in locating an earth moving machine precisely on a tract of land undergoing grading to enable control of the machine to assure that the proper grade pattern is accomplished on the tract. The term "locate" means, in the context of this invention, to determine and define the location of, e.g., an earth moving machine. The term "machine" as used here means a machine which is movable relative to a tract or area and performs a function at the point where it is located, e.g., an earth moving machine which cuts, grades, slopes, picks up, drops or otherwise modifies the earth at its location, modifies a workpiece in a manufacturing operation, provides location at data in surveying, etc. A hand held survey instrument is another important system in which the invention will be embodied. In the sense used here, "machine" may be a part of a larger machine or system. For example, a machine may mean a milling tool, label applicator, etc. The term "tract" will most often be used in reference to a tract of land which is being developed. However, a tract may be a very large geographic area, e.g., the Los Angeles, Calif., basin, etc. A development tract may include several hundred or several thousand acres such as is frequently developed in large westem community projects or industrial projects. In an industrial context, the term "area" will be used in reference to a geometric area upon which the machine operates, one or more points at a time, to accomplish a predetermined result. For example, if a large number of items are being carried by a conveyer belt from a manufacturing operation and it is desired to place a label or marker on each such item, then the area would be that portion of the conveyer belt which is accessible to the machine.